Fixing a Leaking Fuel Tank

October 1, 2016 | By Staff


I bought a nice barn-find 1940 Pontiac recently and after a lot of tinkering I got it running. But even though the gas tank looks pretty good from the outside, it’s leaking. Finding or making a replacement would be very difficult and a used one most likely would be just as bad as the one I’ve got.

Is there a service that restores old tanks? Is there a way to do it myself? I love driving the car. Any advice you can give would be appreciated.


Gas tanks generally rust from the inside out, so they may look quite sound but still be a rusty mess inside. Water doesn’t get up on the gas tank very often except in a storm, but as the fuel is pulled from the tank while you are driving along, moisture-laden air is drawn in to replace it, and when that air hits the cool gasoline the moisture condenses out, often as not on the upper surfaces of the tank. Also, as the car sits in long-term storage the fuel slowly evaporates, exposing the water to do its dirty work.

Fortunately, it is easy to restore your fuel tank yourself. The Eastwood Co. makes a kit that sells for $49.99 that does a good job and doesn’t require an advanced degree to use. It includes a metal wash, a fast etch to give the metal some tooth for the sealer to adhere to, and a couple of bottles of a sealer that prevents rust—is alcohol resistant—and can even seal minor leaks.

Start by draining the tank. Have a fire extinguisher handy, work outdoors or in a well-ventilated place, and don’t smoke anywhere near your fuel tank. If there is a plug in the bottom of the tank, draining it will be easy. All you need is a funnel and a large gas can. Take the filler cap off to allow it to drain more quickly. If the tank does not have a plug you can use a siphon hose available from auto and boat supply stores to draw out the fuel.

Dropping the tank with fuel in it is not a good idea. Gas tanks are big and unwieldy, and quite heavy when full of fuel. Muscling the thing out would be a job, and there is the risk of a spark causing a fire, or worse. Also, never use a flashlight or other electrical device to peer into the tank. A loose spark could be deadly.

Once you have extricated the tank, put it on a couple of sawhorses and fill it with water up into the filler neck and inspect it for leaks. Circle any you find using a china marker, and then drain the tank. Small leaks can be soldered, but don’t try to do it yourself because your tank is still permeated with volatile compounds that can explode when heated. In fact, an empty fuel tank is more dangerous than a full one because of the fumes.

Instead, take the tank to a radiator shop where they can solder the leaks safely. And they may also be able to hot tank it to get all of the loose corrosion out of it. When they are finished, take your tank home and dump a coffee can of miscellaneous nuts and bolts into it, add a little metal wash, shake the tank around thoroughly to break loose any corrosion, and then dump it. Do this repeatedly to all internal surfaces until the metal wash comes out clean.

Let the tank dry and then slosh the metal etch around in it making sure to cover all surfaces. Wash the tank out with water and let it dry thoroughly. A shop vacuum on blow will hasten the drying process, as will compressed air. Finally, pour in the sealer and carefully slosh it into every corner and onto every surface, and then dump the remainder. Let it dry the prescribed amount of time and then add the second bottle and repeat the process.

Once it has cured, you can reinstall the tank. But before you do, make sure the fuel gauge sending unit is in good order. Clean off any corrosion and dip its cork in shellac to help seal and preserve it. Make a new gasket and then install the unit facing in the correct direction. Your tank will be as good as new, and should last for years. To get a fuel tank sealing kit contact:

The Eastwood Company 263 Shoemaker Road Pottstown, PA 19464 |